CENOZOIC ERA. AGE OF MAMMALS. 397 



by inequalities of deposit of the Drift when the ice-sheet 

 retreated. 



Life-System of the Quaternary. 



Plants and Invertebrates. The plants and inver- 

 tebrate animals were mostly identical with those still 

 living. We dismiss these, therefore, with one important 

 remark. Quaternary species are indeed still living ; not, 

 however, in the same place, but much farther north. This 

 indicated that the climate was much colder in the Qua- 

 ternary than now. 



Mammals. It is only in mammals that we find a 

 striking difference as compared with the present time. 

 Those of the Quaternary are peculiar, differing conspicu- 

 ously both from the Tertiary and the living species. We 

 shall take our first examples from Europe, as they have 

 been best studied there. 



Quaternary Mammals of Europe. In Europe they 

 are found sometimes in caves, where in great numbers 

 and of all kinds they have become entombed ; sometimes 

 on river-terraces and old sea-beaches, where their floating 

 carcasses have been stranded and buried ; sometimes in 

 peat-bogs, where, venturing in search of food, they have 

 mired and perished ; and sometimes, as in Arctic regions, 

 in frozen soils, where whole carcasses were sealed up, and 

 are now found perfectly preserved. 



The Mammalian Age culminates here. As already 

 said, the mammalian age seems to culminate in the 

 Quaternary just before its downfall. For example, in 

 England alone, during this time, there lived a great 

 elephant, the mammoth (Elephas primigenius), much 

 larger than any now living ; two species of the rhinoceros 

 and one of the hippopotamus ; three species of oxen, two 

 of which were of gigantic size ; a wild horse ; several 

 species of deer, among which were the reindeer and the 

 great Irish elk, a magnificent animal, eleven feet high to 



